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Branches的Merge操作</a></li><li class="dropdown-item"><!----> <a href="/pages/0c0ca8/" class="nav-link">如何高效阅读嵌入式项目代码</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="前端学习" class="dropdown-title"><!----> <span class="title" style="display:;">前端学习</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/99897f/" class="nav-link">HTML与CSS</a></li><li class="dropdown-item"><!----> <a href="/pages/51542d/" class="nav-link">JS学习</a></li><li class="dropdown-item"><!----> <a href="/pages/803f9d/" class="nav-link">Vue3入门</a></li><li class="dropdown-item"><!----> <a href="/pages/ca4cfb/" class="nav-link">Vue3进阶</a></li><li class="dropdown-item"><!----> <a href="/pages/50e8d3/" class="nav-link">黑马Vue3</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="MFC" class="dropdown-title"><!----> 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class="dropdown-item"><!----> <a href="/pages/28ec23/" class="nav-link">NAND Flash</a></li><li class="dropdown-item"><!----> <a href="/pages/62bf40/" class="nav-link">ARM 处理器</a></li><li class="dropdown-item"><!----> <a href="/pages/1a9374/" class="nav-link">嵌入式基础知识-存储器</a></li><li class="dropdown-item"><!----> <a href="/pages/aac5e3/" class="nav-link">闪存存储和制造技术概述</a></li><li class="dropdown-item"><!----> <a href="/pages/8f6056/" class="nav-link">芯片IO驱动力</a></li><li class="dropdown-item"><!----> <a href="/pages/d146b8/" class="nav-link">主流先进封装技术介绍</a></li><li class="dropdown-item"><!----> <a href="/pages/16f0ba/" class="nav-link">NAND Flash基础</a></li><li class="dropdown-item"><!----> <a href="/pages/90d8d0/" class="nav-link">基于PA算法的FTL引导</a></li><li class="dropdown-item"><!----> <a href="/pages/eb672b/" class="nav-link">SD逻辑擦除和物理擦除</a></li><li class="dropdown-item"><!----> <a href="/pages/747121/" class="nav-link">NAND Flash的SDR、ONFI、DDR接口</a></li><li class="dropdown-item"><!----> <a href="/pages/1eb351/" class="nav-link">【详解】Nand Flash必看知识</a></li><li class="dropdown-item"><!----> <a href="/pages/d2512a/" class="nav-link">【两万字详解】Nand Flash必看知识</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="面经" class="dropdown-title"><!----> <span class="title" style="display:;">面经</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/d69946/" class="nav-link">虎牙C++技术面经</a></li><li class="dropdown-item"><!----> <a href="/pages/29251d/" class="nav-link">金山一面复习</a></li><li class="dropdown-item"><!----> <a href="/pages/c7c01f/" class="nav-link">完美世界秋招 C++ 游戏开发面经(Cpp部分)</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="其它" class="dropdown-title"><!----> <span class="title" style="display:;">其它</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/fa256e/" class="nav-link">博客搭建</a></li><li class="dropdown-item"><!----> <a href="/pages/335531/" class="nav-link">网站收藏箱</a></li></ul></div></div> <!----></nav></div></header> <div class="sidebar-mask"></div> <div class="sidebar-hover-trigger"></div> <aside class="sidebar" style="display:none;"><!----> <nav class="nav-links"><div class="nav-item"><a href="/" class="nav-link">首页</a></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="CPP语言" class="dropdown-title"><!----> <span class="title" style="display:;">CPP语言</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/c5bdd8/" class="nav-link">Cpp之旅</a></li><li class="dropdown-item"><!----> <a href="/pages/279e62/" class="nav-link">Cpp专栏</a></li><li class="dropdown-item"><!----> <a href="/pages/801755/" class="nav-link">Effective_CPP</a></li><li class="dropdown-item"><!----> <a href="/pages/6b2468/" class="nav-link">muduo网络库</a></li><li class="dropdown-item"><!----> <a href="/pages/5f8c9f/" class="nav-link">Unix环境高级编程</a></li><li class="dropdown-item"><!----> <a href="/pages/3f1d21/" class="nav-link">Cpp提高编程</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="计算机基础" class="dropdown-title"><!----> <span class="title" style="display:;">计算机基础</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/7b1cb2/" class="nav-link">计算机网络</a></li><li class="dropdown-item"><!----> <a href="/pages/6048a8/" class="nav-link">操作系统</a></li><li class="dropdown-item"><!----> <a href="/pages/3b34ba/" class="nav-link">数据结构</a></li><li class="dropdown-item"><!----> <a href="/pages/412fe7/" class="nav-link">Linux</a></li><li class="dropdown-item"><!----> <a href="/pages/2dcfa1/" class="nav-link">算法</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="数据库" class="dropdown-title"><!----> <span class="title" style="display:;">数据库</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/efa3f2/" class="nav-link">基础篇</a></li><li class="dropdown-item"><!----> <a href="/pages/ccc445/" class="nav-link">MySql</a></li><li class="dropdown-item"><!----> <a href="/pages/54616e/" class="nav-link">Redis</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="嵌入式软件开发" class="dropdown-title"><!----> <span class="title" style="display:;">嵌入式软件开发</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/d142c2/" class="nav-link">电子嵌入式通信协议</a></li><li class="dropdown-item"><!----> <a href="/pages/4c6bf3/" class="nav-link">深入浅出SSD</a></li><li class="dropdown-item"><!----> <a href="/pages/d3f36a/" class="nav-link">文件系统</a></li><li class="dropdown-item"><!----> <a href="/pages/e0cca7/" class="nav-link">汇编语言</a></li><li class="dropdown-item"><!----> <a href="/pages/fab2d7/" class="nav-link">STM32</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="开发日常" class="dropdown-title"><!----> <span class="title" style="display:;">开发日常</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/e472d1/" class="nav-link">随笔（持续更新）</a></li><li class="dropdown-item"><!----> <a href="/pages/71f6ae/" class="nav-link">Git知识总结</a></li><li class="dropdown-item"><!----> <a href="/pages/db6fb8/" class="nav-link">Git备忘清单</a></li><li class="dropdown-item"><!----> <a href="/pages/e1081f/" class="nav-link">Git 创建删除远程分支</a></li><li class="dropdown-item"><!----> <a href="/pages/777b8a/" class="nav-link">nvm使用小结</a></li><li class="dropdown-item"><!----> <a href="/pages/ee770e/" class="nav-link">虚拟机固定 IP 地址</a></li><li class="dropdown-item"><!----> <a href="/pages/1ab9a6/" class="nav-link">Shell 脚本学习笔记</a></li><li class="dropdown-item"><!----> <a href="/pages/411aa4/" class="nav-link">VScode 插件 CodeGeeX 使用教程</a></li><li class="dropdown-item"><!----> <a href="/pages/0d525d/" class="nav-link">KylinV10 将项目上传至 Github教程</a></li><li class="dropdown-item"><!----> <a href="/pages/907786/" class="nav-link">KylinV10 安装 MySQL 教程（可防踩雷）</a></li><li class="dropdown-item"><!----> <a href="/pages/a2d21e/" class="nav-link">kylinV10-SP1 安装 QT</a></li><li class="dropdown-item"><!----> <a href="/pages/b561cf/" class="nav-link">高并发内存池</a></li><li class="dropdown-item"><!----> <a href="/pages/6ab6d1/" class="nav-link">USBGUARD 项目编译环境配置</a></li><li class="dropdown-item"><!----> <a href="/pages/883f02/" class="nav-link">Power_Destory 项目</a></li><li class="dropdown-item"><!----> <a href="/pages/479472/" class="nav-link">U 盘清除工具编译教程</a></li><li class="dropdown-item"><!----> <a href="/pages/9c4241/" class="nav-link">个人博客代码推送教程</a></li><li class="dropdown-item"><!----> <a href="/pages/3ad765/" class="nav-link">SVN Trunk Branches的Merge操作</a></li><li class="dropdown-item"><!----> <a href="/pages/0c0ca8/" class="nav-link">如何高效阅读嵌入式项目代码</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="前端学习" class="dropdown-title"><!----> <span class="title" style="display:;">前端学习</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/99897f/" class="nav-link">HTML与CSS</a></li><li class="dropdown-item"><!----> <a href="/pages/51542d/" class="nav-link">JS学习</a></li><li class="dropdown-item"><!----> <a href="/pages/803f9d/" class="nav-link">Vue3入门</a></li><li class="dropdown-item"><!----> <a href="/pages/ca4cfb/" class="nav-link">Vue3进阶</a></li><li class="dropdown-item"><!----> <a href="/pages/50e8d3/" class="nav-link">黑马Vue3</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="MFC" class="dropdown-title"><!----> <span class="title" style="display:;">MFC</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/a4b108/" class="nav-link">MFC编程随记</a></li><li class="dropdown-item"><!----> <a href="/pages/41acbd/" class="nav-link">MFC实现ini配置文件的读取</a></li><li class="dropdown-item"><!----> <a href="/pages/951a7a/" class="nav-link">MFC实现点击列表头排序</a></li><li class="dropdown-item"><!----> <a href="/pages/a8598f/" class="nav-link">贴图法美化Button按钮</a></li><li class="dropdown-item"><!----> <a href="/pages/054516/" class="nav-link">MFC使用细节</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="闪存" class="dropdown-title"><!----> <span class="title" style="display:;">闪存</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/b925b8/" class="nav-link">如何高效阅读嵌入式项目代码</a></li><li class="dropdown-item"><!----> <a href="/pages/28ec23/" class="nav-link">NAND Flash</a></li><li class="dropdown-item"><!----> <a href="/pages/62bf40/" class="nav-link">ARM 处理器</a></li><li class="dropdown-item"><!----> <a href="/pages/1a9374/" class="nav-link">嵌入式基础知识-存储器</a></li><li class="dropdown-item"><!----> <a href="/pages/aac5e3/" class="nav-link">闪存存储和制造技术概述</a></li><li class="dropdown-item"><!----> <a href="/pages/8f6056/" class="nav-link">芯片IO驱动力</a></li><li class="dropdown-item"><!----> <a href="/pages/d146b8/" class="nav-link">主流先进封装技术介绍</a></li><li class="dropdown-item"><!----> <a href="/pages/16f0ba/" class="nav-link">NAND Flash基础</a></li><li class="dropdown-item"><!----> <a href="/pages/90d8d0/" class="nav-link">基于PA算法的FTL引导</a></li><li class="dropdown-item"><!----> <a href="/pages/eb672b/" class="nav-link">SD逻辑擦除和物理擦除</a></li><li class="dropdown-item"><!----> <a href="/pages/747121/" class="nav-link">NAND Flash的SDR、ONFI、DDR接口</a></li><li class="dropdown-item"><!----> <a href="/pages/1eb351/" class="nav-link">【详解】Nand Flash必看知识</a></li><li class="dropdown-item"><!----> <a href="/pages/d2512a/" class="nav-link">【两万字详解】Nand Flash必看知识</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="面经" class="dropdown-title"><!----> <span class="title" style="display:;">面经</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/d69946/" class="nav-link">虎牙C++技术面经</a></li><li class="dropdown-item"><!----> <a href="/pages/29251d/" class="nav-link">金山一面复习</a></li><li class="dropdown-item"><!----> <a href="/pages/c7c01f/" class="nav-link">完美世界秋招 C++ 游戏开发面经(Cpp部分)</a></li></ul></div></div><div class="nav-item"><div class="dropdown-wrapper"><button type="button" aria-label="其它" class="dropdown-title"><!----> <span class="title" style="display:;">其它</span> <span class="arrow right"></span></button> <ul class="nav-dropdown" style="display:none;"><li class="dropdown-item"><!----> <a href="/pages/fa256e/" class="nav-link">博客搭建</a></li><li class="dropdown-item"><!----> <a href="/pages/335531/" class="nav-link">网站收藏箱</a></li></ul></div></div> <!----></nav>  <ul class="sidebar-links"><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading open"><span>Cpp之旅</span> <span class="arrow down"></span></p> <ul class="sidebar-links sidebar-group-items"><li><a href="/pages/c5bdd8/" class="sidebar-link">第1章 基础</a></li><li><a href="/pages/88a7db/" class="sidebar-link">第2章 用户自定义类型</a></li><li><a href="/pages/61ffe6/" class="sidebar-link">第3章 模块化</a></li><li><a href="/pages/2dfe3d/" class="sidebar-link">第4章 错误处理</a></li><li><a href="/pages/1cb324/" class="sidebar-link">第5章 类</a></li><li><a href="/pages/fae683/" aria-current="page" class="active sidebar-link">第6章 基本操作</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level2"><a href="/pages/fae683/#_6-1-基本操作" class="sidebar-link">6.1 基本操作</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/pages/fae683/#_6-1-2-转换" class="sidebar-link">6.1.2 转换</a></li><li class="sidebar-sub-header level3"><a href="/pages/fae683/#_6-1-3-成员初始值设定项" class="sidebar-link">6.1.3 成员初始值设定项</a></li></ul></li><li class="sidebar-sub-header level2"><a href="/pages/fae683/#_6-2-拷贝和移动" class="sidebar-link">6.2 拷贝和移动</a><ul class="sidebar-sub-headers"><li class="sidebar-sub-header level3"><a href="/pages/fae683/#_6-2-1-拷贝容器" class="sidebar-link">6.2.1 拷贝容器</a></li><li class="sidebar-sub-header level3"><a href="/pages/fae683/#_6-2-2-移动容器" class="sidebar-link">6.2.2 移动容器</a></li></ul></li><li class="sidebar-sub-header level2"><a href="/pages/fae683/#_6-3-资源管理" class="sidebar-link">6.3 资源管理</a></li><li class="sidebar-sub-header level2"><a href="/pages/fae683/#_6-4-建议" class="sidebar-link">6.4 建议</a></li></ul></li><li><a href="/pages/2cdace/" class="sidebar-link">第7章 模板</a></li><li><a href="/pages/619376/" class="sidebar-link">第8章 概念和泛型编程</a></li><li><a href="/pages/48ac45/" class="sidebar-link">第9章 标准库</a></li></ul></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Cpp专栏</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Effetcive_CPP</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>muduo网络库</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Unix环境高级编程</span> <span class="arrow right"></span></p> <!----></section></li><li><section class="sidebar-group collapsable depth-0"><p class="sidebar-heading"><span>Cpp提高编程</span> <span class="arrow right"></span></p> <!----></section></li></ul> </aside> <div><main class="page"><div class="theme-vdoing-wrapper "><div class="articleInfo-wrap" data-v-06225672><div class="articleInfo" data-v-06225672><ul class="breadcrumbs" data-v-06225672><li data-v-06225672><a href="/" title="首页" class="iconfont icon-home router-link-active" data-v-06225672></a></li> <li data-v-06225672><span data-v-06225672>CPP语言</span></li><li data-v-06225672><span data-v-06225672>Cpp之旅</span></li></ul> <div class="info" data-v-06225672><div title="作者" class="author iconfont icon-touxiang" data-v-06225672><a href="javascript:;" data-v-06225672>霜晨月</a></div> <div title="创建时间" class="date iconfont icon-riqi" data-v-06225672><a href="javascript:;" data-v-06225672>2023-11-24</a></div> <!----></div></div></div> <!----> <div class="content-wrapper"><div class="right-menu-wrapper"><div class="right-menu-margin"><div class="right-menu-title">目录</div> <div class="right-menu-content"></div></div></div> <h1><img src="">第6章 基本操作<!----></h1> <!----> <div class="theme-vdoing-content content__default"><h1 id="cpp之旅-学习笔记-第6章-基本操作"><a href="#cpp之旅-学习笔记-第6章-基本操作" class="header-anchor">#</a> Cpp之旅（学习笔记）第6章 基本操作</h1> <h2 id="_6-1-基本操作"><a href="#_6-1-基本操作" class="header-anchor">#</a> 6.1 基本操作</h2> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">class</span> <span class="token class-name">X</span><span class="token punctuation">{</span>
<span class="token keyword">public</span><span class="token operator">:</span>
    <span class="token function">X</span><span class="token punctuation">(</span>Sometype<span class="token punctuation">)</span><span class="token punctuation">;</span>			<span class="token comment">// &quot;普通的构造函数&quot;: 创建一个对象</span>
    <span class="token function">X</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>					<span class="token comment">// 默认构造函数</span>
    <span class="token function">X</span><span class="token punctuation">(</span><span class="token keyword">const</span> X<span class="token operator">&amp;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>			<span class="token comment">// 拷贝构造函数</span>
    <span class="token function">X</span><span class="token punctuation">(</span>X<span class="token operator">&amp;&amp;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>					<span class="token comment">// 移动构造函数</span>
    X<span class="token operator">&amp;</span> <span class="token keyword">operator</span><span class="token operator">=</span><span class="token punctuation">(</span><span class="token keyword">const</span> X<span class="token operator">&amp;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>	<span class="token comment">// 拷贝赋值操作符：清空目标对象并拷贝</span>
    X<span class="token operator">&amp;</span> <span class="token keyword">operator</span><span class="token operator">=</span><span class="token punctuation">(</span>X<span class="token operator">&amp;&amp;</span><span class="token punctuation">)</span><span class="token punctuation">;</span>		<span class="token comment">// 移动赋值操作符：清空目标对象并移动</span>
    <span class="token operator">~</span><span class="token function">X</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">;</span>					<span class="token comment">// 析构函数：清理资源</span>
    <span class="token comment">//...</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br></div></div><p><strong>在下面5种情况下，对象会被移动或拷贝：</strong></p> <ul><li>赋值给其他对象。</li> <li>作为对象初始化。</li> <li>作为函数的实参。</li> <li>作为函数的返回值。</li> <li>作为异常。</li></ul> <p><strong>如果希望显示地使用函数的默认实现：在函数后面加上 <code>=default</code></strong></p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">class</span> <span class="token class-name">Y</span><span class="token punctuation">{</span>
<span class="token keyword">public</span><span class="token operator">:</span>
    <span class="token function">Y</span><span class="token punctuation">(</span>Sometype<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token function">Y</span><span class="token punctuation">(</span><span class="token keyword">const</span> Y<span class="token operator">&amp;</span><span class="token punctuation">)</span> <span class="token operator">=</span> <span class="token keyword">default</span><span class="token punctuation">;</span>	<span class="token comment">// 我确实需要默认的拷贝构造函数</span>
    <span class="token function">Y</span><span class="token punctuation">(</span>Y<span class="token operator">&amp;&amp;</span><span class="token punctuation">)</span> <span class="token operator">=</span> <span class="token keyword">default</span><span class="token punctuation">;</span>		<span class="token comment">// 也确实需要默认的移动构造函数</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><ul><li>一旦显示地指定了某些函数地默认形式，编译器就不会再为函数生成其他默认定义了。</li> <li>当类中含有指针成员时，最好显示地指定拷贝操作和移动操作。如果不这样做，当编译器生成地默认函数试图delete指针对象时，系统将发生错误。</li></ul> <p><strong>如果不想生成目标操作函数：在函数后面加上<code>=delete</code></strong></p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">class</span> <span class="token class-name">Shape</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span><span class="token operator">:</span>
    <span class="token function">Shape</span><span class="token punctuation">(</span><span class="token keyword">const</span> Shape<span class="token operator">&amp;</span><span class="token punctuation">)</span> <span class="token operator">=</span><span class="token keyword">delete</span><span class="token punctuation">;</span>		<span class="token comment">// 禁止拷贝</span>
    Shape<span class="token operator">&amp;</span> <span class="token keyword">operator</span><span class="token operator">=</span><span class="token punctuation">(</span><span class="token keyword">const</span> Shape<span class="token operator">&amp;</span><span class="token punctuation">)</span> <span class="token operator">=</span><span class="token keyword">delete</span><span class="token punctuation">;</span>
    <span class="token comment">//...</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
<span class="token keyword">void</span> <span class="token function">copy</span><span class="token punctuation">(</span>Shape<span class="token operator">&amp;</span> s1<span class="token punctuation">,</span> <span class="token keyword">const</span> Shape<span class="token operator">&amp;</span> s2<span class="token punctuation">)</span>
<span class="token punctuation">{</span>
    s1 <span class="token operator">=</span> s2<span class="token punctuation">;</span>							<span class="token comment">// 错误：Shape禁止拷贝</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br></div></div><ul><li>试图使用=delete的函数会在编译时报错；=delete可以用于禁用任意函数，并非仅仅用于禁用基础成员函数。</li></ul> <h3 id="_6-1-2-转换"><a href="#_6-1-2-转换" class="header-anchor">#</a> 6.1.2 转换</h3> <p>接受单个参数的构造函数同时定义了从参数类型到类类型的转换。</p> <p>例如：complex提供了一个接受double类型的参数的构造函数：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">class</span> <span class="token class-name">complex</span> <span class="token punctuation">{</span>
    <span class="token keyword">double</span> re<span class="token punctuation">,</span>im<span class="token punctuation">;</span>		<span class="token comment">// 成员变量：两个双精度浮点数</span>
<span class="token keyword">public</span><span class="token operator">:</span>
    <span class="token function">complex</span><span class="token punctuation">(</span><span class="token keyword">double</span> r<span class="token punctuation">,</span><span class="token keyword">double</span> i<span class="token punctuation">)</span><span class="token operator">:</span>re<span class="token punctuation">{</span>r<span class="token punctuation">}</span><span class="token punctuation">,</span>im<span class="token punctuation">{</span>i<span class="token punctuation">}</span><span class="token punctuation">{</span><span class="token punctuation">}</span>	<span class="token comment">// 用两个标量构建该复数</span>
    <span class="token function">complex</span><span class="token punctuation">(</span><span class="token keyword">double</span> r<span class="token punctuation">)</span><span class="token operator">:</span>re<span class="token punctuation">{</span>r<span class="token punctuation">}</span><span class="token punctuation">,</span>im<span class="token punctuation">{</span><span class="token number">0</span><span class="token punctuation">}</span><span class="token punctuation">{</span><span class="token punctuation">}</span>				<span class="token comment">// 用一个标量构建该复数</span>
    <span class="token function">complex</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token operator">:</span>re<span class="token punctuation">{</span><span class="token number">0</span><span class="token punctuation">}</span><span class="token punctuation">,</span>im<span class="token punctuation">{</span><span class="token number">0</span><span class="token punctuation">}</span><span class="token punctuation">{</span><span class="token punctuation">}</span>						<span class="token comment">// 默认的复数是：{0，0}</span>
    <span class="token comment">//...</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
complex z1 <span class="token operator">=</span> <span class="token number">3.14</span><span class="token punctuation">;</span>	<span class="token comment">// z1变成 {3.14，0.0}</span>
complex z2 <span class="token operator">=</span> z1<span class="token operator">*</span><span class="token number">2</span><span class="token punctuation">;</span>	<span class="token comment">// z2变成 z1*{2.0,0} == {6.28,0.0}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br></div></div><ul><li>这种转换有时似乎合情理，有时则不然。</li></ul> <p>例如：Vector提供了一个接受int类型的参数构造函数：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">class</span> <span class="token class-name">Vector</span><span class="token punctuation">{</span>
<span class="token keyword">private</span><span class="token operator">:</span>
    <span class="token keyword">double</span><span class="token operator">*</span> elem<span class="token punctuation">;</span>
    <span class="token keyword">int</span> sz<span class="token punctuation">;</span>
<span class="token keyword">public</span><span class="token operator">:</span>
    <span class="token function">Vector</span><span class="token punctuation">(</span><span class="token keyword">int</span> s<span class="token punctuation">)</span><span class="token operator">:</span>elem<span class="token punctuation">{</span><span class="token keyword">new</span> <span class="token keyword">double</span><span class="token punctuation">[</span>s<span class="token punctuation">]</span><span class="token punctuation">}</span><span class="token punctuation">,</span>sz<span class="token punctuation">{</span>s<span class="token punctuation">}</span>
    <span class="token punctuation">{</span>
        <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">!=</span> s<span class="token punctuation">;</span> <span class="token operator">++</span>i<span class="token punctuation">)</span>
            elem<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
    <span class="token punctuation">}</span>
    <span class="token operator">~</span><span class="token function">Vector</span><span class="token punctuation">(</span><span class="token punctuation">)</span><span class="token punctuation">{</span><span class="token keyword">delete</span><span class="token punctuation">[</span><span class="token punctuation">]</span> elem<span class="token punctuation">;</span><span class="token punctuation">}</span>
    <span class="token comment">// ...</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
Vector v1 <span class="token operator">=</span> <span class="token number">7</span><span class="token punctuation">;</span>		<span class="token comment">// 可行：v1有7个元素</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br></div></div><ul><li>通常情况下，该语句的执行结果并非如我们的预期，标准库vector禁止这种int到vector的转换。</li></ul> <p>解决该问题的办法是只允许显示进行类型转换：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">class</span> <span class="token class-name">Vector</span><span class="token punctuation">{</span>
<span class="token keyword">public</span><span class="token operator">:</span>
    <span class="token keyword">explicit</span> <span class="token function">Vector</span><span class="token punctuation">(</span><span class="token keyword">int</span> s<span class="token punctuation">)</span><span class="token punctuation">;</span>	<span class="token comment">// 不能隐式地将int转化为Vector</span>
    <span class="token comment">// ...</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
Vector <span class="token function">v1</span><span class="token punctuation">(</span><span class="token number">7</span><span class="token punctuation">)</span><span class="token punctuation">;</span>		<span class="token comment">// 可行：v1有7个元素</span>
Vector v2 <span class="token operator">=</span> <span class="token number">7</span><span class="token punctuation">;</span>		<span class="token comment">// 错误：不能隐式地将int转化为Vector</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br></div></div><ul><li>关于类型转换地问题，complex只是一小部分，大多数类型地情况与Vector类似。</li></ul> <p><strong>所以除非你有充分地理由，否则最好把接受单个参数的构造函数声明成explicit的。</strong></p> <h3 id="_6-1-3-成员初始值设定项"><a href="#_6-1-3-成员初始值设定项" class="header-anchor">#</a> 6.1.3 成员初始值设定项</h3> <p>定义类的数据成员时，可以提供默认的初始值，称其为默认成员初始值设定项。</p> <p>如下：修订版本的complex</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">class</span> <span class="token class-name">complex</span> <span class="token punctuation">{</span>
    <span class="token keyword">double</span> re <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
    <span class="token keyword">double</span> im <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>	<span class="token comment">// 表示两个默认值为0.0的double类型的成员</span>
<span class="token keyword">public</span><span class="token operator">:</span> 
    <span class="token function">complex</span><span class="token punctuation">(</span><span class="token keyword">double</span> r<span class="token punctuation">,</span> <span class="token keyword">double</span> i<span class="token punctuation">)</span> <span class="token operator">:</span> re<span class="token punctuation">{</span>r<span class="token punctuation">}</span><span class="token punctuation">,</span> im<span class="token punctuation">{</span>i<span class="token punctuation">}</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>	<span class="token comment">// 从两个标量{r,i}构造complex</span>
    <span class="token function">complex</span><span class="token punctuation">(</span><span class="token keyword">double</span> r<span class="token punctuation">)</span> <span class="token operator">:</span> re<span class="token punctuation">{</span>r<span class="token punctuation">}</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>					<span class="token comment">// 从一个标量{r,0}构造complex</span>
    <span class="token function">complex</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span><span class="token punctuation">}</span>									<span class="token comment">// 默认值为{0，0}的complex</span>
    <span class="token comment">// ...</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br></div></div><p>对于所有构造函数没有提供初始值的成员，默认初始值都会起作用。</p> <h2 id="_6-2-拷贝和移动"><a href="#_6-2-拷贝和移动" class="header-anchor">#</a> 6.2 拷贝和移动</h2> <p>默认情况下，我们可以拷贝对象，不论是用户自定义类型的对象还是内置类型的对象。</p> <p>拷贝的默认含义是逐成员地复制，即依次复制每个成员。</p> <h3 id="_6-2-1-拷贝容器"><a href="#_6-2-1-拷贝容器" class="header-anchor">#</a> 6.2.1 拷贝容器</h3> <p>当一个类被作为资源句柄时，换句话说，当这个类负责通过指针访问一个对象时，采用默认的逐成员复制方式通常意味着会产生灾难性的错误。</p> <p>逐成员复制的方式会违反资源句柄的约束条件。</p> <p>例如：默认拷贝将产生Vector的一份拷贝，而这个拷贝所指向的元素与原来的元素是同一个：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">void</span> <span class="token function">bad_copy</span><span class="token punctuation">(</span>Vector v1<span class="token punctuation">)</span>
<span class="token punctuation">{</span>
    Vector v2 <span class="token operator">=</span> v1<span class="token punctuation">;</span>	<span class="token comment">// 将v1的表层拷贝到v2</span>
    v1<span class="token punctuation">[</span><span class="token number">0</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token number">2</span><span class="token punctuation">;</span>		<span class="token comment">// v2[0]也变成了2</span>
    v2<span class="token punctuation">[</span><span class="token number">1</span><span class="token punctuation">]</span> <span class="token operator">=</span> <span class="token number">3</span><span class="token punctuation">;</span>		<span class="token comment">// v1[1]也变成了3</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br></div></div><p>假设v1包含4个元素，则结果如下图所示：</p> <p><img alt="1699599237447" data-src="https://cdn.jsdelivr.net/gh/xiaose-code/Pictures@main/img/1699599237447.webp" loading="lazy" class="lazy"></p> <p>类对象的拷贝操作可以通过两个成员来定义：拷贝函数与拷贝赋值操作符：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">class</span> <span class="token class-name">Vector</span> <span class="token punctuation">{</span>
<span class="token keyword">public</span><span class="token operator">:</span>
    <span class="token function">Vector</span><span class="token punctuation">(</span><span class="token keyword">int</span> s<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token operator">~</span><span class="token function">Vector</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token punctuation">{</span> <span class="token keyword">delete</span><span class="token punctuation">[</span><span class="token punctuation">]</span> elem<span class="token punctuation">;</span> <span class="token punctuation">}</span>
    
    <span class="token function">Vector</span><span class="token punctuation">(</span><span class="token keyword">const</span> Vector<span class="token operator">&amp;</span> a<span class="token punctuation">)</span><span class="token punctuation">;</span>				<span class="token comment">// 拷贝构造函数</span>
    Vector<span class="token operator">&amp;</span> <span class="token keyword">operator</span><span class="token operator">=</span><span class="token punctuation">(</span><span class="token keyword">const</span> Vector<span class="token operator">&amp;</span> a<span class="token punctuation">)</span><span class="token punctuation">;</span>		<span class="token comment">// 拷贝赋值操作符</span>
    
    <span class="token keyword">double</span><span class="token operator">&amp;</span> <span class="token keyword">operator</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">(</span><span class="token keyword">int</span> i<span class="token punctuation">)</span><span class="token punctuation">;</span>
    <span class="token keyword">const</span> <span class="token keyword">double</span><span class="token operator">&amp;</span> <span class="token keyword">operator</span><span class="token punctuation">[</span><span class="token punctuation">]</span><span class="token punctuation">(</span><span class="token keyword">int</span> i<span class="token punctuation">)</span> <span class="token keyword">const</span><span class="token punctuation">;</span>
    
    <span class="token keyword">int</span> <span class="token function">size</span><span class="token punctuation">(</span><span class="token punctuation">)</span> <span class="token keyword">const</span><span class="token punctuation">;</span>
<span class="token keyword">private</span><span class="token operator">:</span>
    <span class="token keyword">double</span><span class="token operator">*</span> elem<span class="token punctuation">;</span>
    <span class="token keyword">int</span> sz<span class="token punctuation">;</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br><span class="line-number">11</span><br><span class="line-number">12</span><br><span class="line-number">13</span><br><span class="line-number">14</span><br><span class="line-number">15</span><br><span class="line-number">16</span><br></div></div><p>对Vector来说，拷贝构造函数的正确定义应该首先为指定数量的元素分配空间，然后把元素复制到空间中。这样复制完成后，每个Vector就拥有自己的元素拷贝了：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token class-name">Vector</span><span class="token double-colon punctuation">::</span><span class="token function">Vector</span><span class="token punctuation">(</span><span class="token keyword">const</span> Vector<span class="token operator">&amp;</span> a<span class="token punctuation">)</span> <span class="token operator">:</span> elem <span class="token punctuation">{</span><span class="token keyword">new</span> <span class="token keyword">double</span><span class="token punctuation">[</span>a<span class="token punctuation">.</span>sz<span class="token punctuation">]</span><span class="token punctuation">}</span><span class="token punctuation">,</span> sz<span class="token punctuation">{</span>a<span class="token punctuation">.</span>sz<span class="token punctuation">}</span>	<span class="token comment">//拷贝构造函数，分配元素所需要的空间</span>
<span class="token punctuation">{</span>
    <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">!=</span> sz<span class="token punctuation">;</span> <span class="token operator">++</span>i<span class="token punctuation">)</span>
        elem<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">=</span> a<span class="token punctuation">.</span>elem<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>在这个示例中，v2=v1的结果现在可以表示成：</p> <p><img alt="1699599716792" data-src="https://cdn.jsdelivr.net/gh/xiaose-code/Pictures@main/img/1699599716792.webp" loading="lazy" class="lazy"></p> <p>除了拷贝构造函数，我们还需要一个拷贝赋值操作符：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code>Vector<span class="token operator">&amp;</span> Vector<span class="token double-colon punctuation">::</span><span class="token keyword">operator</span><span class="token operator">=</span><span class="token punctuation">(</span><span class="token keyword">const</span> Vector<span class="token operator">&amp;</span> a<span class="token punctuation">)</span> 	<span class="token comment">// 拷贝赋值操作</span>
<span class="token punctuation">{</span>
    <span class="token keyword">double</span><span class="token operator">*</span> p <span class="token operator">=</span> <span class="token keyword">new</span> <span class="token keyword">double</span><span class="token punctuation">[</span>a<span class="token punctuation">.</span>sz<span class="token punctuation">]</span><span class="token punctuation">;</span>
    <span class="token keyword">for</span><span class="token punctuation">(</span><span class="token keyword">int</span> i <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span> i <span class="token operator">!=</span> a<span class="token punctuation">.</span>sz<span class="token punctuation">;</span> <span class="token operator">++</span>i<span class="token punctuation">)</span>
        p<span class="token punctuation">[</span>i<span class="token punctuation">]</span> <span class="token operator">=</span> a<span class="token punctuation">.</span>elem<span class="token punctuation">[</span>i<span class="token punctuation">]</span><span class="token punctuation">;</span>
    <span class="token keyword">delete</span><span class="token punctuation">[</span><span class="token punctuation">]</span> elem<span class="token punctuation">;</span>							<span class="token comment">// 删除旧元素</span>
    elem <span class="token operator">=</span> p<span class="token punctuation">;</span>
    sz <span class="token operator">=</span> a<span class="token punctuation">.</span>sz<span class="token punctuation">;</span>
    <span class="token keyword">return</span> <span class="token operator">*</span><span class="token keyword">this</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br><span class="line-number">9</span><br><span class="line-number">10</span><br></div></div><p>其中，名字this被预定义在成员函数中，它指向调用该成员函数的那个对象。</p> <p>元素拷贝发生在旧元素被删除之前，所以如果在拷贝的过程中抛出异常，Vector的旧值可得以保留。</p> <h3 id="_6-2-2-移动容器"><a href="#_6-2-2-移动容器" class="header-anchor">#</a> 6.2.2 移动容器</h3> <p>对于大容量的容器，拷贝过程有可能消耗巨大。</p> <p>当给函数传递对象时，可通过使用引用类型来减少拷贝对象的代价，但是无法返回局部对象的引用（函数的调用者都没机会和返回结果碰面，局部对象就被销毁了）。</p> <p>我们相比于拷贝一个Vector对象，更希望移动它。</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token keyword">class</span> <span class="token class-name">Vector</span> <span class="token punctuation">{</span>
    <span class="token comment">// ...</span>
    <span class="token function">Vector</span><span class="token punctuation">(</span><span class="token keyword">const</span> Vector<span class="token operator">&amp;</span> a<span class="token punctuation">)</span><span class="token punctuation">;</span>			<span class="token comment">// 拷贝构造函数（复制构造）</span>
    Vector<span class="token operator">&amp;</span> <span class="token keyword">operator</span><span class="token operator">=</span><span class="token punctuation">(</span><span class="token keyword">const</span> Vector<span class="token operator">&amp;</span> a<span class="token punctuation">)</span><span class="token punctuation">;</span>	<span class="token comment">// 拷贝赋值操作符（复制赋值）</span>
    
    <span class="token function">Vector</span><span class="token punctuation">(</span>Vector<span class="token operator">&amp;&amp;</span> a<span class="token punctuation">)</span><span class="token punctuation">;</span>					<span class="token comment">// 移动构造函数</span>
    Vector<span class="token operator">&amp;</span> <span class="token keyword">operator</span><span class="token operator">=</span><span class="token punctuation">(</span>Vector<span class="token operator">&amp;&amp;</span> a<span class="token punctuation">)</span><span class="token punctuation">;</span>		<span class="token comment">// 移动赋值操作符</span>
<span class="token punctuation">}</span><span class="token punctuation">;</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br><span class="line-number">6</span><br><span class="line-number">7</span><br><span class="line-number">8</span><br></div></div><p>基于上述定义，编译器将选择移动构造函数来执行从函数中移出返回值的任务。</p> <p>定义Vector移动构造函数的过程非常简单：</p> <div class="language-CPP line-numbers-mode"><pre class="language-cpp"><code><span class="token class-name">Vector</span><span class="token double-colon punctuation">::</span><span class="token function">Vector</span><span class="token punctuation">(</span>Vector<span class="token operator">&amp;&amp;</span> a<span class="token punctuation">)</span> <span class="token operator">:</span> elem <span class="token punctuation">{</span>a<span class="token punctuation">.</span>elem<span class="token punctuation">}</span><span class="token punctuation">,</span> sz<span class="token punctuation">{</span>a<span class="token punctuation">.</span>sz<span class="token punctuation">}</span>
<span class="token punctuation">{</span>
    a<span class="token punctuation">.</span>elem <span class="token operator">=</span> <span class="token keyword">nullptr</span><span class="token punctuation">;</span>	<span class="token comment">//现在a中没有任何元素</span>
    a<span class="token punctuation">.</span>sz <span class="token operator">=</span> <span class="token number">0</span><span class="token punctuation">;</span>
<span class="token punctuation">}</span>
</code></pre> <div class="line-numbers-wrapper"><span class="line-number">1</span><br><span class="line-number">2</span><br><span class="line-number">3</span><br><span class="line-number">4</span><br><span class="line-number">5</span><br></div></div><p>符号&amp;&amp;的意思是”右值引用“，右值的含义与左值正好相反。</p> <p>左值的大致含义是 ”能出现在赋值操作符左侧的内容“，因此右值大致上就是无法为其赋值的值，比如函数调用返回的一个整数就是右值。进一步地，右值引用地含义就是引用了一个别人无法赋值地内容，所以我们可以安全地”窃取“它的值。</p> <p>移动构造函数不接受const实参：毕竟移动构造函数最终要删除它实参中的值。</p> <h2 id="_6-3-资源管理"><a href="#_6-3-资源管理" class="header-anchor">#</a> 6.3 资源管理</h2> <p>通过定义构造函数、拷贝操作、移动操作和析构函数，程序员就能对受控资源（比如容器中元素）的生命周期进行完全控制。</p> <p>内存也不是唯一的一种资源。资源是指任何在使用前需要获取与（显示或隐式）释放的东西，除了内存，还有锁、套接字、文件句柄和线程句柄等非内存资源。</p> <p>在Cpp标准库中，RAII无处不在：例如，内存（string、vector、map、unordered_map等）、文件（ifstream、ofstream等）、线程（thread）、锁（lock_guard、unique_lock等）和通用对象（通过unique_ptr和shared_ptr访问）。</p> <h2 id="_6-4-建议"><a href="#_6-4-建议" class="header-anchor">#</a> 6.4 建议</h2> <ol><li>尽量让对象的构造、拷贝（复制）、移动和销毁、在掌控之中；</li> <li>同时定义所有的基本操作，或者什么都不定义；</li> <li>如果默认的构造函数、赋值操作符和析构函数符合要求、那么让编译器负责生成它们；</li> <li>如果类含有指针成员，考虑这个类是否需要用户自定义或者删除析构函数、拷贝函数及移动函数；</li> <li>默认情况下，把单参数的构造函数声明成explicit的；</li> <li>如果默认拷贝函数不适合当前类型，则重新定义或禁止拷贝函数；</li> <li>用传值的方式返回容器（依赖拷贝消除和移动以提高效率）；</li> <li>避免显示使用std::copy()；</li> <li>对于容量较大的操作数，使用const引用作为参数类型；</li> <li>使用RAII管理所有资源——内存和非内存资源；</li></ol></div></div> <!----> <div class="page-edit"><!----> <!----> <div class="last-updated"><span class="prefix">上次更新:</span> <span class="time">2024/6/3 14:54:44</span></div></div> <div class="page-nav-wapper"><div class="page-nav-centre-wrap"><a href="/pages/1cb324/" class="page-nav-centre page-nav-centre-prev"><div class="tooltip">第5章 类</div></a> <a href="/pages/2cdace/" class="page-nav-centre page-nav-centre-next"><div class="tooltip">第7章 模板</div></a></div> <div class="page-nav"><p class="inner"><span class="prev">
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